Since an operating system (hereinafter referred to as OS) for an information processor is contained in an external storage unit, such as an HDD, if the HDD itself or the content of the HDD is destroyed, the information processor cannot be started.
As a precaution against such an accident, a duplicate of the contents of the external storage unit is usually retained in a tape unit or the like. Such a duplicate is called a backup.
A description is given of a procedure for generating a backup with reference to FIG. 10. Initially, a tape unit for backup is mounted on an information processor equipped with an HDD (step S81). Then, data in the HDD is copied to backup tapes (step S82). In this method, two backup tapes are employed, i.e., a tape to which the OS of the HDD is copied and a tape to which user's data is copied. Hereinafter, the former is called an OS installation tape and the latter is called a user's data tape.
When the HDD has a fault after generation of the backup, a user executes a procedure shown in FIG. 11, as a countermeasure against the fault.
Initially, the user checks the extent of the fault (step S91). When the fault is destruction of data stored in the HDD, the user immediately sets the OS installation tape in a tape drive unit which is mounted on the information processor (step S93). When the HDD itself is destroyed physically, the user replaces the HDD with another one (step S92) and sets the OS installation tape (step S93). Thereafter, the user starts an OS installing tool from the OS installation tape (step S94), whereby the OS is installed in the HDD (step S95).
Further, the user resets the system of the information processor according to his work (step S96). Thereafter, the user sets the user's data tape (step S97) and restores the data from this tape into the HDD (step S98).
Another countermeasure against the fault in the external storage unit is to duplicate the external storage unit. More specifically, two external storage units having equal performances are prepared, and data of the same contents are written in both the external storage units simultaneously. In this case, even when one of the external storage units is out of order, the user can operate the information processor continuously using the other storage unit operating normally.
However, the conventional method employing the backup tapes have the following drawbacks.
Firstly, when the external storage unit is destroyed, since the external storage unit must be replaced with another one, the operation of the information processor is stopped until the replacement is completed.
Secondly, when the contents of the external storage unit are destroyed, after reinstallation of the OS, the user resets the system of the information processor according to his work, so that resetting of the present file is necessary. For the resetting, the operation of the information processor must be stopped for half a day.
On the other hand, the method of duplicating the external storage unit has the following drawback.
In this method, since data of the same contents are written simultaneously, two (first and second) external storage units having equal writing performances must be used. Hence, it is impossible to use an expensive and high-speed HDD as the first storage unit while using an inexpensive and low-speed optical disk for the second storage unit. Therefore, the cost of the external storage units is doubled according to the amount of data duplicated.